Laser-induced color reversal on metal surfaces in acetic acid solution

Laser coloring for decoration and visual attraction has been widely used in daily life. To fulfill the requirements of timely correction or modification of colors, color erasure has also become an important part in marking technology. The thickness of the oxide layer and the concentration of oxygen elements are key factors affecting the quality of color erasing. The conventional method is to erase the color in air, which is difficult to remove the oxide film. Acetic acid, as an environment-friendly solution, which provides a low oxygen environment and can undergo chemical reactions with titanium dioxide under laser heating, is selected as a liquid environment for laser-induced color erasure. Oxygen concentration in the erased area decreases from more than 50% to 10%. The color difference Delta E ab * between the erased area and original metal surface is around 1.4, which shows almost no difference to the naked eyes. Furthermore, the color difference Delta E ab * between laser re-coloring and laser coloring before the erasure is around 1.5, which means that the re-coloring under the same laser processing parameters after the erasure maintains a high level of consistency with the colors initially drawn. Here we successfully realize the reversal process from laser coloring to laser erasure and laser re-coloring on metal surfaces. This technology has considerable applications in the field of anti-counterfeiting and information storage. Meanwhile, acetic acid assisted laser color erasing as a safe and green method greatly improves the erasure quality and enhances the development of laser color marking technology.